1. Field of the Invention
The present invention relates to a scanner sharing device for enabling a plurality of computers to share one scanner device.
2. Description of the Related Art
In an office or other such environment, there are cases where it is requested to have a plurality of personal computers to share a single peripheral device such as a printer or scanner device. In such a case, the method of connecting a plurality of personal computers with one server to thereby connect the peripheral device with the plurality of personal computers through the server, the method of connecting a network-supported printer etc. to a network made up of a plurality of personal computers, the method of connecting a plurality of personal computers and a peripheral device through a USB switch, etc. are being used. In particular, the method of using a USB switch is often used as it is inexpensive and is capable of easily realizing requests.
As a USB switch enabling a plurality of personal computers to share a peripheral device, there is for example a USB host switching device disclosed in Japanese Unexamined Patent Publication No. 2003-195991. This USB host switching device is provided with a USB device connector for a USB device to be connected thereto, a plurality of USB host connectors for personal computers and other USB hosts to be connected thereto, and a changeover switch for selecting any one connector from the plurality of USB host connectors and connecting the selected USB host connector with the USB device connector. The changeover switch is manually operated or the USB host connector connected to a powered up USB host is automatically detected so as to connect the USB host connector to which a powered up USB host is connected and the USB device connector. Note that, if there are plurality of powered up USB connectors, one USB host connector is selected according to a predetermined priority ranking.
Further, there is also an automatic USB switch capable of automatic switching even when a plurality of powered up personal computers are connected with the automatic USB switch. In such a USB switch, a USB controller monitors for the presence of a data signal between a personal computer connected with a USB device through the USB switch and the USB device. If there is no data signal transmitted for a constant period of time (for example, approximately 10 seconds), it judges that the connection with the USB device can be released. If there is a connection request from a different personal computer when the connection with the USB device can be released, it switches the connection so as to connect this personal computer with the USB device.
In the case where one printer is shared by a plurality of powered up personal computers, the data signal for one job is sent continuously from a personal computer to the printer. Therefore, the personal computer connected with the printer will not be switched during one job even if an automatic USB switch is used.
However, in the case of a scanner device, a certain amount of time is required from the time the command to start scanning is sent to until the scanner device starts scanning. During this period, a read data signal is not transmitted. Further, due to jam, document reload or other causes, the communication for the data signal is sometimes interrupted for a certain amount of time even during a job. In the case of a scanner device, in this way, there is the possibility that one job cannot be judged as being completed even if the communication for the data signal is interrupted for a certain amount of time in such a matter. As such, when using an automatic USB switch to enable a plurality of personal computers to share one scanner device, there are times when a connection request will be sent from a different personal computer in a state where no data signal is being transmitted and therefore the USB controller will judge that the present connection between the personal computer and the scanner device is releasable and release the connection with the scanner device to the different personal computer before the job is completed. As a result, there is the problem in that the operation of the USB switch will become unstable when switching again right after switching a connection, and the protection from switching during execution of a job will become unreliable.